The Global Influence of Mantle Temperature on Intraplate Magmatism

Mantle convection governs broad-scale Earth processes such as plate tectonics, volatile cycling and dynamic topography. Intraplate volcanic activity is often attributed to warm upwelling mantle and is therefore a useful tool in understanding how the planform of mantle convection changes through time. Here, I compiled a comprehensive global geochemical database of >20,000 Neogene and Quaternary intraplate volcanic samples. By comparing this database to surface-wave tomographic models, I show that >90% of intraplate volcanic regions occur above lithosphere <100 km thick and anomalously hot mantle at 100-200 km depths. Shear-wave velocity anomalies, ΔVs, at these depths positively correlate with incompatible element concentrations in mafic intraplate rocks. Therefore, both mafic rock compositions and shear wave velocities are sensitive to mantle temperature variations. This correlation decreases appreciably at depths >200 km, which demonstrates that the composition of intraplate volcanic rocks are sensitive to thermochemical variations in the uppermost mantle.  

Forward and inverse modelling of rare earth elements are used to estimate asthenospheric temperatures and lithospheric thicknesses beneath each intraplate volcanic province. These geochemical results are compared with asthenospheric temperature and lithospheric thickness estimates from tomographic models. A positive correlation is observed between geochemical and tomographic potential temperature estimates. The relationship between melt composition and mantle temperature can be obscured on local scales by mantle heterogeneity and alterations to the primary melt on the way to the surface. However, a global analysis reveals coherent signals between these observations, and so the location and composition of intraplate magmatism can play an important role in predicting past mantle conditions. I will also show initial results for the eastern Australian Cenozoic volcanic province.